1. Field of the Invention
Many radio receivers provide users with a convenience feature for automatically searching for broadcast frequencies in a band of interest and selecting only those broadcast signals received with sufficient quality to be considered “listenable” for sustained audio output. This feature, known as search tuning in a “seek”, or “scan” (with a truncated period of sustained audio output) operating mode is typically engaged by pressing a button, which then causes the tuner to automatically advance to the next frequency on which a station may broadcast, and evaluate whether a “listenable” broadcast is being received. If so, the tuner remains on that frequency. Otherwise, the tuner advances to the next available frequency.
2. Description of the Prior Art
For example, U.S. Pat. No. 5,613,230 discloses an AM radio receiver which includes search tuning such as seek or scan tuning features whose stop thresholds for locking onto a received frequency are adapted to environmental conditions. In the preferred embodiment, wideband signal strength, preferably derived from the automatic gain control of the radio frequency amplifier, provides a representative signal to the microprocessor for adapting the thresholds used during search tuning. The thresholds are increased when significant energy is present in the AM band and proportioned to the level of that energy. The decision logic of the microprocessor adapts thresholds according to the tuned signal strength, to wideband signal strength, to nighttime operation during which ionosphere conditions increase transmissibility of distant radio signals, and to intermediate frequency (IF) count validity to reduce the probability of stopping on audibly noisy frequencies when the RF signal environment is noisy.
Energy Harvesting
The harvesting of Radio Frequency (RF) energy is extremely important for Radio Frequency Identification (RFID), security monitoring and remote sensing as well as other uses. Some harvesting devices may be tuned to a specific frequency (RFID), while others take advantage of the ambient energy (remote sensing) and others simply sense frequencies for security purposes.
Recharging devices using an RF electromagnetic field radiated into free space have been described. U.S. Pat. No. 6,127,799 describes a charge storage device that is charged by exposing the charge storage device to an RF electromagnetic field radiated into free space. The charge storage device includes one or more antennas disposed on the device and adapted to receive the radiated RF electromagnetic field. One or more rectifiers are connected to the antennas for rectifying the received RF electromagnetic field into a DC output current. The DC output current produced by the rectifier is used to energize the charge storage device.
As disclosed in U.S. Pat. No. 6,127,799, the antennas may be one or more dipole antennas which are combined to form at least two subsets of dipole antenna element arrays, wherein one subset may be oriented at an acute or a right angle with respect to at least one other subset. The antennas or dipole antennas may be placed on more than one outside surface of the charge storage device which enclose an acute or a right angle with respect to each other. The antennas in the energy harvesting circuit of U.S. Pat. No. 6,127,799 are designed for a specific frequency.
U.S. patent application Ser. No. 10/624,051 by Mickle et al entitled, “Energy Harvesting Circuits and Associated Methods” discloses an energy harvesting circuit that has an inherently tuned antenna, with at least portions of the energy harvesting circuit structured to provide regenerative feedback into the antenna to thereby establish an effective antenna area substantially greater than the physical area
A major problem with the prior art is that the energy harvesting circuits cannot efficiently harvest RF energy at frequencies outside the design specific frequency of the antenna.
There is a need for energy harvesting circuits that can harvest RF energy from a broad RF spectrum.
Furthermore, there is a need for energy harvesting circuits that can harvest RF energy from a broad RF spectrum by having the ability to be tuned to broadcast frequencies (or other ambient frequencies) in a band of interest and select the broadcast signal that maximizes the RF energy.
Also, there is a need for small remote power charger device that has a means for receipt of transmitted energy from the environment and energizing power storage devices on an object of interest wherein the power charger device automatically searches for broadcast frequencies in a band of interest and selects the broadcast signal that maximizes the RF energy.